The present invention generally relates to a light wavelength converting apparatus for converting divergent rays into parallel rays.
Conventionally, it is known to generate a second higher harmonic for converting the wavelength of laser light in half through the application of the nonlinear optical effect as disclosed in Japanese Laid-Open Patent Application Tokkaisho No. 61-72222, etc.
An apparatus for converting the wavelength of laser light in half will be described hereinafter with reference to FIG. 9 through FIG. 11.
Referring to FIG. 9, a light wavelength converting element 3 is composed of a nonlinear optical crystalline substrate 1 and an optical waveguide 2 disposed on the nonlinear optical crystalline substrate 1, with reference numerals 4, 5, 6, 7 designating a light incidence portion of the optical wavelength converting element 3, a semiconductor laser, a collimator lens, and a focusing lens.
When the rays 8 converged by the collimator lens 6 and the focusing lens 7 are introduced into the light incidence portion 4, the second higher harmonic (hereinafter referred to as SH rays) is produced by the nonlinear optical effect provided by the optical waveguide 2. It is to be noted that the primary rays 18 pass through the optical waveguide 2.
The SH rays 9 are known as Cherenkov radiation light which is transmitted in the form of semi-circular divergent rays 10 as shown in FIG. 11. The SH rays 9 are transmitted at an angle A in the y direction relation to the waveguide 2 and at an angle B in the x direction.
However, because the SH rays 9 which are divergent as described hereinabove are hard to use, luminous flux means for transmitting the divergent rays 10 as parallel rays is required.
A conventional optical wavelength converting apparatus will be described hereinafter with reference to FIG. 12.
The SH rays 9 radiating from an SHG element (not shown) are collimated in the x-direction by the cylindrical convex lens 12. Then, they are diverged by the cylindrical concave lens 13 and become rays of light 16 divergent in the y-direction. Then, the expanse thereof in the y-direction is collimated by the cylindrical convex lens 14 into parallel rays 17. However, the above-described structure requires three cylindrical lenses, thus resulting in a large apparatus. Furthermore, the above-described structure is effective when used with a spot light source. Completely parallel rays could not be provided when used with a linear light source which has a waveguide passage length that transmits Cherenkov radiation light.